Electrically heatable primary catalytic converter

ABSTRACT

An electrically heatable starter catalytic converter (5) has a metallic housing (6) in which is arranged the actual catalyst (7) exposed to the exhaust gas flow, an electric resistance heating (8) and an electric connection line (10) that enters the housing (6) through an opening (9). The invention is characterized in that the electric connection line (10) is a metal-clad cable with at least one inner lead (11) electrically insulated from the metal cladding by a mineral (13). The inner lead (11) frictionally engages the electric resistance heating (8), and the metal cladding (12) enters the metallic housing (6) through the opening (9) and is welded or soldered to the edge of the opening (9) in a gas-tight manner.

BACKGROUND OF THE INVENTION

The invention relates to an electrically heatable primary catalyticconverter having a metal housing, a catalyst provided in the housing andexposed to an exhaust gas stream, an electrical resistive heater and aconnecting lead fed to the heater from the outside through an opening.

Primary catalytic converters of this type are known in a plurality ofembodiments and have proved their value. However, it is disadvantageousthat the electrical connecting lead is a problem. Thus, plastic-coatedconnecting leads are unsuited for a moisture- and gas-type connection athigh temperatures and in corrosive media, as for example in the exhaustfrom internal combustion engines. In addition, clamp or screwconnections made of conventional conducting materials, such as copper,nickel, or other alloys, cannot be used since they cannot ensurepermanently reliable electrical connections because of the oxidationand/or corrosion of the interfaces. In particular, high contactresistances develop. On the one hand, if precious metals or preciousmetal coatings are used on the conducting materials, high costs result.On the other hand, the temperature in the connecting area of the primarycatalytic converter can only be reduced by costly design measures. Inview of the limited space for accommodation of such primary catalyticconverters, functional disadvantages must be taken into account as aresult of such measures, for example limitation of the exhaust gasstream to areas remote from the contacts.

SUMMARY OF THE INVENTION

Hence, the goal of the invention is to provide a permanently reliableelectrical connection. This goal is achieved in an electrical primarycatalytic converter providing the electrical connecting lead as a metaljacket lead with at least one internal conductor insulated therefromelectrically by a mineral. The metal jacket lead is guided through theopening into the metal housing and connected therewith in a gas-tightmanner by welding or soldering along the edge of the opening.

Thus, for example, a metal jacketed lead with at least one internalconductor insulated from it electrically by means of a mineral is usedas the electrical connecting lead. The internal conductor is positivelyconnected with the electrical resistance heater, for example, by weldingor soldering (Wolfram (tungsten) inert gas (WIG) laser or spot welding).The metal jacketed lead is also fed through an opening in the metalhousing and connected with the latter in a gas-tight manner by weldingor soldering along the edge of the opening. Thus assurance is providedin simple fashion that firstly the gas tightness of the housing isguaranteed and secondly the connecting lead can be connected reliably ina permanent fashion despite being located in a hot and corrosiveenvironment.

Further improvements on the invention are possible. In particular, ascrew or clamp connection to the internal conductor can be welded,soldered, or crimped at the cold end of the metal jacketed lead, namelythe lead located outside the housing. In addition, an electricallyinsulating sheath can be mounted over the connection at the cold end asmoisture protection. Preferably, a mineral electrical insulating layeris located between the metal jacket and the internal conductor, saidlayer consisting for example of MgO and/or Al₂ O₃, quartz, or glass. Theinternal conductor can be made of an alloy containing copper and/oraluminum and/or iron and/or nickel. Preferably, the aluminum content ofthe internal conductor is 3-10 weight percent, the iron content is up to4 weight percent, and the nickel content is up to 5 weight percent.Preferably, both ends of the metal jacketed lead are sealed tightly toprotect against loss of insulation as well as the penetration of gases,moisture, and contamination that reduce the insulation resistance.Synthetic resins are particularly suitable for this purpose at the coldend, while ceramic adhesives are used at the hot or cold end, especiallyadhesives based on aluminum oxide or magnesium oxide. In addition,ceramic molded bodies can be used, glued or glazed to the metal jacketand internal conductor.

The metal jacket conductors according to the invention make it possibleto adjust the temperature gradients over the length and adjust the restof the design in such fashion that a temperature that does not exceed250° C. prevails at their cold ends. Consequently, an economical plasticinsulated copper cable can be used for this application. Theembrittlement of the insulation of the connecting lead and the influenceof high temperature and vibration in the prior art no longer occur. Inaddition, the metal jacketed lead permits a dimensionally stable bendingcontour of the connecting lead without additional retaining elements.

The metal jacketed lead used according to the invention can be used notonly on primary catalytic converters, but also at all locations wherethere is a hot and corrosive environment.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will now be described with reference tothe drawing in greater detail, said drawing showing a schematic crosssection through a primary catalytic converter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The primary catalytic converter, designated as a whole by 5, has ahousing 6 as well as the catalyst itself 7 located inside, provided withan electrical resistance heater, represented schematically by 8. Anelectrical connecting lead 10 is fed into housing 6 through an opening9.

This electrical connecting lead 10 is designed as a metal jacketed leadwith at least one electrically insulated internal conductor 11 insulatedby a mineral 13, for example MgO or Al₂ O₃. In the embodiment shown, asingle internal conductor 11 is provided, concentric with respect toouter metal jacket 12. The electrically insulating mineral 13 isprovided therebetween. The metal jacketed lead 10 is passed throughopening 9 into the interior of housing 6 and connected along the edge ofopening 9 by welding 15 so that a gas-tight feedthrough is obtained.Internal conductor 11 is likewise connected with electrical resistanceheater 8 by a welded connection 16.

At the end of the metal jacketed lead 10 that is located outside thehousing 6, i.e. the cold end, a screw or clamp connection designatedschematically as a whole by 14 is provided. Both ends are sealed by aceramic adhesive, not shown, so that the mineral insulator is protectedagainst moisture, gas, and contamination.

We claim:
 1. Electrically heatable primary catalytic convertercomprising a metal housing, a catalyst located in the metal housing andexposed to an exhaust stream, an electrical resistance heater providedin the metal housing, and an electrical connecting lead fed to theelectrical resistance heater from the outside of the housing through anopening, wherein the electrical connecting lead is a metal jacket leadhaving at least one internal conductor and a metal jacket surroundingthe at least one internal conductor over a major portion of the lengthof the at least one internal conductor and insulated therefromelectrically by a mineral, the internal conductor being positivelyconnected with the electrical resistance heater, and the metal jacketbeing guided through the opening into the metal housing and connectedtherewith in a gas-tight manner by welding or soldering along an edge ofthe opening.
 2. Primary catalytic converter according to claim 1,wherein at least an end of the metal jacketed lead located in thehousing is sealed.
 3. Primary catalytic converter according to claim 2,wherein the end of the metal jacketed lead located in the housing issealed by ceramic adhesive.
 4. Primary catalytic converter according toclaim 2, wherein at least the end of metal jacketed lead located in thehousing is sealed by a molded body, said molded body being connectedwith the metal jacket and the internal conductor by gluing or glazing.5. Primary catalytic converter according to claim 4, wherein the moldedbody is a ceramic molded body.
 6. Primary catalytic converter accordingto claim 1, wherein the internal conductor is positively connected withthe electrical resistance heater by welding or brazing.
 7. Primarycatalytic converter according to claim 1, wherein the internal conductorconsists of an alloy containing copper and/or aluminum and/or ironand/or nickel.
 8. Primary catalytic converter according to claim 1,wherein the internal conductor consists of a chromium-nickel high-gradesteel or high-temperature nickel-based alloy.
 9. Primary catalyticconverter according to claim 1, wherein an aluminum content of theinternal conductor is 3-10 weight percent, an iron content is up to 4weight percent, and an nickel content is up to 5 weight percent. 10.Primary catalytic converter according to claim 3, wherein the end of themetal jacketed lead located in the housing is sealed by ceramic adhesivecomprising Al₂ O₃ or MgO.
 11. Primary catalytic converter according toclaim 1, wherein the metal jacketed lead is so constructed as to permita dimensionally stable bending contour of the metal jacketed leadwithout additional retaining elements.
 12. Primary catalytic converteraccording to claim 1, wherein the metal jacketed lead has a lengthpermitting a cold end of the at least one internal conductor opposite anend located in the metal housing to have a temperature during use notexceeding 250° C.